Hey, Rob!
We currently have a star grain AP design for our second stage as we intend to balloon launch. It is very similar to Ky's Go Fast rocket. We intend to cast ourselfs and I must say I got alot of help from Richard Nakka and his work. We used some software to pallpark the design then We switched over to the calculator. We will do some test very soon. We also intend to move to liquid propulsion after perfecting our SRB Motors. Rocket motor testing should comence just after Oct. 31.

Does anyone know how well a film cooled copper engine would do, I know AA do Stainless, I'm just thinking of ease of working with, availiability, price etc.
1ft long tube of 316SS is roughly US$57
1ft long tube of C122 Copper same size as above US$46

I'm thinking a film cooled liquid engine might be the easiest and quickest way to make and test a liquid engine. My thoughts why....

*No O-ring seals, everything is silver soldered or welded together, being the injector to the chamber etc.

*You could easily spin the chamber/nozzle etc. like AA, then its just a matter of making the injector

*Time to make would be resonably quick

I'm not sure if anyone does seamless copper tube in large OD's though as might be required.
I did see on AA webite that they lost 19lbs from their old engine by switching to the SS one.

I actually got halfway through the original X-Prize entry process before backing off that after reviewing how credible an entry I could mount.

I really should have completed my entry, I was hardly the *least* credible candidate.

The N-prize is a really interesting stepping stone. The prize money and budget allowance preclude a lot of options.

However, I am aiming at building something capable of putting 3 cubesats into orbit for under $30k or $10k each, total operational charges. The launcher ends up haveing to cost some where in the $1k- $3k range.

While I might be able to launch something to meet the N-Prize from New Zealand, I hope to eventually launch from Fiji or Samoa.

Anyways, my ideas revolve around a Bull cannon for the first stage, a Meth/Lox aerospike with submerged cooling for the second stage and probably some sort of orbital insertion stage depending on where the numbers end up.

With 95% of the launch system never leaving the ground I have no idea which category I end up in

The problem with more stages will be the growth factor increasing the launcher to unreasonable size for the amount of fuel we are limited to. The fellow with the R-Candy rocket is closer to the requirements however you have to look harder at the orbital insertion velosity. The R-Candy ISP is to low an ISP for power to weight vs fuel and even with AP propellant you will have a tough time reaching orbital velosity with out increasing the growth to an unreasonable number. This is why we use the Light Gas Gun for the final stage because it can impart large velosity without a major effect in growth factor. The down side is the increase in energy imparted to the satellite is substancial and requires a new way of thinking. Our balloon launch is to reduce the amount of fuel required and no other reason and we use solid fuel for the same reason. I would love to use liquid fuel but really guy's we have to look at the fuel requirements to win the prize. I would love to disscuss this at length here and work this out with anyone that is willing. Face it guy's the falcon 1 was about the smallest rocket that can make orbit with our current tech. If you use the square cube law and reduce it's size you will see what I am getting at it's the fuel. The falcon 1 is a perfect example of what we can do, use that as a model and srink it to it's smallest size and see what you come up with. It wont be cheap or eazy. If we can come up with more realistic hardware people will start taking the N-Prize more seriously. We have to strip everything down to the very limits to really do this. I invite anyone interested to shoot holes in this.

How about easier storable liquid fuels, such as H2O2 and Butane (pressurized into a Liquid) with Balloon launch? Isp can easily exceed 300, so we could only have to lift maybe 20kg to launch a small 100g sat. Imaginative use of Soda bottles and Cardboard tubing is encouraged. In fact, a plastic bottle probably could contain liquid Butane.

To respond to Monroe, and to anyone in general...
First, one of my sayings is: "Rocket Science is like Religion Except We Don't Kill Each Other". I mean that we each tend to develop an investment in whatever technology, methods we've been studying and are reluctant to abandon it.

So, my "faith" is that only a liquid bi-propellant rocket launched from ground level can do it. Balloons are too much bother, drift out of control by winds, and do not buy much in way of less propellant requirement. Also, propellant can be the cheapest component of a launcher.

Lox seems the only logical choice for the oxidizer, and saturated hydrocarbon like butane, propane,etc for the fuel. For special reasons, alcohol or E-85 might be ok for the first stage.

And that it should be 3 stages: first to get above enough of the atmosphere for vacuum optimized upper stage engines to work, second, for a high acceleration velocity increase to perhaps 2-3 km/sec, then third to, with lower acceleration, reach orbit (or escape) velocity.

The mass I've calculated for N Prize is less than 60 kg GLOW (gross liftoff weight), and with the engine thrust of each stage 120-180 kg first stage, and 15 kg second, and 3 kg for 3rd.

I'm assuming vacuum Isp over 250 for ther upper 2 stages, and after testing 3rd stage engine first, will be able to scale the rest of the launcher.

The Isp can be determined by measuring C* at sea level because it requires measuring the chamber pressure from a known flow rate through a known throat area, and it may indicate an Isp of 275 or so, the minimum practical being 250.

The initial design of an optical guidance is done, and a hover test of it is to be done after recruiting one or two "committed volunteer participants",
people prepared to join the effort, work on the building, tests of the launcher components according to plans being formalized.

I am beginning to think that a balloon launch may not be such a good idea. If a balloon mechanism is developed, which would take 3-5 years, I can see it as a good way to save fuel. The cost of keeping track of the balloon system would outweigh the savings in fuel. Existing technologies would make it easier to launch straight from the ground.

I have been doing some research on propellants, and found that gaseous Oxygen from a tank and plain petrol would be the cheapest combination (and simplest to build). We need fuel that does the job for little money, not necessarily the best performance. Just a thought...

It doesn't hav to be recovered. A latex weather balloon could do the trick.

Once problem could be stability, and preventing the rocket from launching into an orbit facing every other peice of junk up there, but it would possibly be possible to design the 0-stage so that it is aerodynamically stable (such as JPAs Ascender).

A high-altitude launch increase Isp, leading to less weight for the same payload. I'm of the opinion that H2O2 and Butane should be used, due to their storability. It would perhaps be best to simply cool the Butane, but pessurizing works as well.

(I haven't actually built any of these rockets... yet, so all of the performence and such I post is purely theoretical.)